At present, there are a certain number of techniques for authenticating handwritten signatures based essentially on measurements of correlation between characteristics of a signature to be authenticated and preliminarily acquired reference characteristics of authorized persons.
The current authentication techniques can be classified under two major categories: a posteriori authentication (or post-authentication) techniques and “real-time” authentication techniques.
The first category of techniques is based on an analysis of characteristics of the signature entered (the size and/or the shape of the letters for example) on the writing surface on which the signature is entered (embossed features created by the entering of the signature on a paper document for example) after the signature has been entered.
The second category of techniques is based on an analysis of characteristics of the signature obtained as and when the signature is entered (the pressure of the writing instrument on the writing surface and/or acceleration of the writing instrument during the signing operation for example), which can be combined with characteristics of the first category of techniques.
This second category of techniques requires the implementation of technical means during the real-time entering of the signature such as for example the use of an accelerometer on the writing instrument, or a pressure sensor on the writing surface.
One of the most important goals to be achieved for these techniques for authenticating of a handwritten signature pertains to the level of security provided, this level being essentially related to the number of characteristics analyzed.
Indeed, the greater the number of characteristics analyzed, the greater is the reliability of the authentication.
By contrast, the greater the number of characteristics analyzed, the higher are the costs of implementation since the means used to obtain these characteristics as well as the means for processing the obtained characteristics have to be numerous, with a view to subsequent authentication.
Thus, among current techniques, it can be seen that those implemented for “large-scale” consumer products (such as graphic tablets) are based on a fairly restricted number of characteristics, for reasons of cost, whereas those implemented in professional products (such as signature tablets) are based on a fairly large number of characteristics and entail an equally high cost of implementation but a higher level of security.
For example, there are “real-time” authentication techniques based on the analysis of characteristics such as a 2D representation of the signature entered, associated with a parameter representing the pressure of the writing instrument on the writing surface and/or a parameter representing the acceleration of the writing instrument along all three axes of space. These techniques are relatively costly because they call for the use of sensors both on the writing surface and on the writing instrument. Furthermore, they also call for complex operations for processing the different captured pieces of data, so that it is possible to then perform the measurements of correlation and thus authenticate the handwritten signature entered.
One drawback of current techniques for authenticating of a handwritten signature therefore lies in the resolution of the cost/security trade-off, i.e. in the choice of greater complexity for a greater level of security or the converse choice.
Thus, there is a need to propose a technique of electronic authentication of a handwritten signature which can provide a maximum level of security without substantially increasing the complexity or the cost of implementation.